ON a balmy summer's evening at Burnley in August 2014, Diego Costa was booked on his first appearance for Chelsea.

Diego Costa did not bite Gareth Barry but his dark side still puts Chelsea future in doubt

Everyone kind of had an indication of what they were getting then - just in case they hadn't noticed the fiery Spaniard's style of football at Atletico Madrid.

That night at Turf Moor, the Chelsea manager Jose Mourinho described the decision to book his new £32 million striker for diving as unfair, and defended his style of play, as the Special One did throughout his second reign at the club, and right up until the final sour weeks, when relations between the two had turned icy.

And there on Saturday night at Goodison Park was Mourinho's successor Guus Hiddink, some 19 months on, still defending Diego's style of play, just the 21 bookings and one sending off later.

But also, crucially, 34 goals later.

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Twenty of those helped Chelsea land the Premier League title last year, 11 in his last 16 this season have hauled them out of the danger of relegation and kept their season from being even more of a catastrophe and embarrassment than it is already.

Because Chelsea got what they paid for with Costa when they splashed out that £32 million.

The dark side of Diego. The elbows, and barges, the gouges, the foot left in slightly too long, the fingers jabbing. The constant complaints from minute one of a match to minute 90. The wide-eyed expressions of hurt and outrage when a foul is perpetrated against him - never mind that he probably provoked it. The incessant in the face moaning to referees.

Of course, plenty of Chelsea fans love Costa for this.

You only have to listen to the chants of "Diego, Diego" that ring around Stamford Bridge every home game, and the songs of the travelling supporters.

They love the Brazilian-born Spaniard.

They love him because he fights (literally), he battles, he hates to lose, he works hard, he loves to score goals. He cares.

Diego Costa appears to bite Gareth Barry and gesture at Everton fans

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Chelsea forward Diego Costa appears to bite Gareth Barry after earlier gesturing at fans as he left the field at half time during the Blues' FA Cup tie against Everton at Goodison Park

There was a brief interruption to that love affair when Costa was suspected of being one of the "rats" Mourinho referred to just before he was sacked.

But Costa soon won over most of the fans again because he so clearly wants to play, plays when injured, begs to play according to Hiddink, who sometimes has to hold his striker back.

And without Costa, Chelsea are a blunt instrument, something easily brushed aside.

When he went off injured against Paris St Germain on Wednesday night, their Champions League chances were gone.

Gone was the snarling physical presence up front, the leader, the target. The hope.

It was like watching a balloon deflate. Chelsea literally have no one else.

Of course, some Chelsea fans are irritated by him. By his constant bookings and suspensions, by his constant arguing, the bordering on illegality and sometimes plain illegal methods. Opposition fans hate him.

There are plenty more who had a naughty side.

But Costa will probably be gone in the summer, his longing to go back to Atletico still strong, and Chelsea without Champions League football next year. For Chelsea he will take some replacing.

One factor that goal record shows, as do Chelsea's performances when Costa is on the field, is that the 27 year old is a very good player.